The technical field of this invention is vehicle brake by wire systems.
A brake by wire system separates the input and control apparatus of the braking system from the actuators by one or more electrical communication lines. Thus there is no direct transmission of force from the vehicle operator to the brake actuators. Such systems are therefore designed with care to provide built in dependability of the components; and one method of providing such dependability is redundancy. But redundancy also increases cost, and it is thus desirable to achieve the redundancy while minimizing this extra cost.
An important element of any braking system, including one according to this invention, is that providing driver input for brake apply, typically the brake pedal. In a hydraulic brake system, this may be a typical mechanical device against which a driver may push a force to apply the brakes through the hydraulic system, with possible power assist. But in a brake by wire system, the brake pedal must be provided with a sensor to detect some aspect of pedal movement and generate an electric signal for the controller that indicates driver intent. Typical sensors used for this task are travel or position sensors and applied force sensors. Each has its own characteristics that may enhance a brake by wire system.
The braking system of this invention provides the capability of both travel and force sensors on a brake apply input member such as a brake pedal and also provides redundancy in sensors by providing the signal from a sensor responsive to travel or position of the brake apply input member to a first controller and the signal from a sensor responsive to force applied to a brake apply input member to a second controller. The first and second controllers are connected by a bi-directional communication link whereby each controller may communicate its received one of the sensor signals to the other controller. In at least one of the controllers, linearized versions of the signals are combined for the generation of first and second brake apply command signals for communication to brake apply units. If either controller does not receive one of the sensor signals from the other, it nevertheless generates its brake apply command signal on the basis of the sensor signal provided directly to it. In a preferred embodiment of the system, a controller combines the linearized signals by choosing the largest in magnitude.